Extended range proportional valve

ABSTRACT

An extended range proportional valve which can control rates of mass flow over continuous low, intermediate and high ranges has a pilot member mounted on an armature of a solenoid which can be dithered onto and off of a pilot opening in a main valve member which seals a main valve opening to control mass flow rates over the low range by varying the duty cycle and/or frequency of a pulse width modulated current in the solenoid coil. Intermediate and high flow rates are achieved by dithering the pilot valve member with a duty cycle and/or frequency sufficient to raise the main valve member relatively short and relatively long respective distances from the main valve seat.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a valve of the proportional flow typeoperated by an electrical solenoid. More particularly, this inventionrelates to a valve having a high turn down ratio, i.e., one which cancontrol flow rates ranging from very low, through intermediate, to veryhigh magnitudes.

[0002] Proportional flow valves find utility in performing mixing andmeasurement functions. For example, proportional flow valves are used toaccurately blend gasolines to achieve desired characteristics, such asparticular octane ratings, to mix hot and cold water to obtain a desiredtemperature, and to dispense compressible and noncompressible fluids,including liquids such as gasoline, and gases such as air and naturalgas. Depending on the application for which a proportional flow valve isto be used, it may be necessary to maintain constant flow rates of avery low magnitude as well as constant flow rates of a very highmagnitude, and constant flow rates of an intermediate magnitude betweensaid high an low magnitudes.

[0003] In some prior art proportional valves, a main valve member islifted off of and lowered onto a main valve seat to open and close thevalve. The main valve member can be mounted at the center of adiaphragm. Such a valve is shown in U.S. Pat. No. 5,676,342. This valvepermits a rate of fluid flow through the valve proportional to theamount of electric current flowing through the coil of the solenoidactuator controlling the valve. In this type of arrangement, theactuator behaves in a linear matter, i.e., the force produced by thesolenoid armature is linearly proportional to the current applied to thesolenoid. As a result, the solenoid armature works in a linear manneragainst a closing spring which constantly urges the valve member towardthe valve seat. In this way, the distance which the valve member ismoved away from the valve seat is proportional to the amount of currentapplied to the solenoid.

[0004] Atop the main valve member is a pilot valve seat which surroundsa pilot opening through the center of the main valve member. The plungerof a solenoid above the main valve member carries a pilot valve memberwhich is lowered to seal the pilot valve opening in the main valvemember and raised to open the pilot valve opening in the main valvemember.

[0005] There is also a bleed opening in the housing or diaphragm, orthrough another channel, through which fluid can flow between areservoir chamber above the diaphragm and an inlet chamber below thediaphragm. This bleed opening is smaller than the pilot opening. Whenthe pilot opening is sealed by the plunger, fluid from the inlet portenters the inlet chamber below the diaphragm and passes through thebleed opening in the diaphragm to the reservoir above the diaphragm. Thefluid above the diaphragm urges the diaphragm downwardly toward the mainvalve seat thereby sealing a main valve opening surrounded by the mainvalve seat, and closing the valve. When the solenoid is actuated to liftthe plunger off of the pilot opening, fluid above the diaphragm isdrained through the pilot opening faster than it can enter through thesmaller bleed opening thereby lessening the pressure above the diaphragmand causing fluid pressure from the inlet below the diaphragm to forcethe diaphragm upward thereby lifting the main valve member off of themain valve seat for opening the valve.

[0006] The valve of the above mentioned U.S. Pat. No. 5,676,342 has beenfound to admirably perform its function. However when very low flowrates are to be maintained, the plunger is moved to a position whichenables the diaphragm to lift the main valve member just slightly off ofthe main valve opening. At this time, the pressure differential betweenthe areas above and below the diaphragm is so great that the main valvemember tends to jump when lifted off of the main valve seat therebypreventing attainment of very low flow rates. This occurrence denotesthe bottom end of the flow vs. current characteristic. That is, in avalve where flow rate is uniformly diminished by decreasing the currentapplied to the solenoid coil, flow is abruptly shut off when thesolenoid coil current is reduced to a level whereat the main valvemember is forced onto the main valve seat.

[0007] Conversely, while the main valve member is in engagement with themain valve seat and the current induced in the coil of a proportionalsolenoid valve is gradually increased, a level is reached whereat themain valve member jumps off of the main valve seat to a position whereatthe lowest possible flow rate for that valve is achieved. Although thisminimum flow rate can be optimized through careful selection of designparameters for the valve's components, it can not be improvedsufficiently in cases where precise low flow rates are required.

[0008] It is also known in the art to operate a solenoid valve at aconstant high flow rate by applying to the valve solenoid a full wave ACcurrent for displacing the main valve member from the main valve seat,and at a constant low flow rate by rectifying the AC current to obtain ahalf-wave AC signal which, when applied to the solenoid coil, enablesfluid to pass through the pilot opening but does not provide sufficientlifting force to enable the main valve member to be lifted off of themain valve seat. Such a valve is the subject of U.S. Pat. No. 4,503,887to Johnson et al.

[0009] It is further known in the art to vary the degree of displacementof a pilot valve member from a pilot valve seat in a proportional valveby applying power to the valve's solenoid coil in the form of aperiodically pulsed DC current, the amount of current varying with thelength of “on” and “off” times of the pulses, sometimes referred to aspulse width modulation. Pulse width modulation for this purpose isdisclosed in U.S. Pat. No. 5,294,089 to LaMarca and U.S. Pat. No.5,676,342 to Otto et al.

[0010] None of the foregoing approaches has provided a solution to theproblem of making a proportional solenoid valve with a high turn-downration, i.e., one which enables continuous variation of flow rate fromvery high and intermediate levels during which the main valve member isdisplaced from the main valve seat, to low levels during which the mainvalve member remains seated for sealing the main valve opening, andfluid flow is limited to passage through the pilot opening.

SUMMARY OF THE INVENTION

[0011] According to the invention, low flow rates are achieved over acontinuous range, without lifting the main valve member off of the mainvalve seat, through pulse width and/or frequency modulation of thecurrent applied to the coil of a proportional solenoid valve. For lowflow rates, e.g., gas flowing at a rate of 0.5 standard cubic feet perminute (scfm) to 5.0 scfm, the solenoid armature or plunger isoscillated or dithered onto and off of the pilot valve seat on the mainvalve member with a duty cycle during which the pilot opening is exposedto inlet fluid under pressure for a portion of the cycle, and the pilotopening is closed for the balance of the cycle thereby maintaining themain valve member on the main valve seat and limiting fluid flow to apath through the pilot opening. For increasingly greater flow rates, theduty cycle of the solenoid armature is adjusted to increase theproportion of the cycle during which the pilot opening is exposed to thefluid, and thereby increase the rate of fluid flow through the pilotopening.

[0012] As the rate of fluid flow approaches a level that can allowcontrol of the displacement of the main valve member from the main valveseat without the problem of jumping which is encountered at lower flowrates, the duty cycle of the solenoid current is further adjusted toenable the pilot valve to remain open long enough to raise the mainvalve member from the main valve seat a distance corresponding to adesired intermediate rate of flow whereat the rate of flow through thepilot opening is supplemented by limited flow through the main valveopening. Flow at intermediate mass flow rates is permitted as the mainvalve member is lifted to a position a short distance from the mainvalve seat. Higher flow rates, to which the contribution of flow throughthe pilot opening becomes insignificant, are achieved as the main valvemember is lifted further away from the main valve seat.

[0013] It is therefore an object of the invention to provide a singleproportional flow valve which can provide continuous variation of flowrates over a range heretofore unrealizable.

[0014] Another object of the invention is to provide a proportional flowvalve with a solenoid actuator which can be energized by a currenthaving a variable duty cycle for dithering a pilot valve member onto andoff of a pilot seat on a main valve member for enabling a continuousrange of low flow rates through a pilot opening in the valve withoutraising the main valve member from the main valve seat.

[0015] Still another object of this invention is to provide apparatusfor modulating flow through the pilot opening in the seated main valvemember without reaching the critical flow rate at which open the mainvalve member is lifted of off the main valve seat.

[0016] A further object of the invention is to provide a valve of thetype described above wherein the duty cycle and/or frequency of thepulse width modulated solenoid current can be adjusted to enable thepilot valve to remain open long enough to raise the main valve memberfrom the main valve seat in degrees corresponding to a desired rate ofintermediate or high volume fluid flow.

[0017] Still another object of the invention is to maintain continuitybetween low flow, intermediate flow, and high flow rates in aproportional solenoid valve as a transition takes place from a range oflow flow rates only through the pilot opening (main valve closed)through intermediate flow rates having significant components passingthrough both the pilot and main valve openings, to high flow rates whichoccur principally through the main valve opening.

[0018] Other and further objects of the invention will be apparent fromthe following drawings and description of a preferred embodiment of theinvention in which like reference numerals are used to indicate likeparts in the various views.

DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a cross sectional view of a proportional flow valve inaccordance with the preferred embodiment of the invention, the solenoidactuator being deenergized and the valve closed.

[0020]FIG. 2 is a view similar to FIG. 1, but showing the valve whilepermitting a low range of mass flow rates.

[0021]FIG. 3 is a view similar to FIG. 1, but showing the valve whilepermitting an intermediate range of mass flow rates.

[0022]FIG. 4 is a view similar to FIG. 1 but showing the valve whilepermitting a high range of mass flow rates.

[0023]FIG. 5 is a schematic block diagram depicting the power supply forthe solenoid of FIGS. 1-4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] Referring to FIGS. 1-4 of the drawings, a proportional flow valve10 chosen to illustrate the present invention includes a valve body 12having a fluid inlet port 14, a fluid outlet port 16, and main valveseat 18 surrounding a main orifice 20. The outlet port 16 resides withina hollow elbow having a right angular bend 24 which joins a horizontalsection 22 and an a vertical section 28, the latter terminating at themain valve seat 18.

[0025] A main valve unit 30 includes a main valve member 32 slidablymounted within vertical section 28 of outlet port 16 for reciprocalaxial movement. The main valve member 32 has a generally circular crosssection and axially extending circumferentially spaced parallel vanes34, two of which can be seen in the drawings. The outer circumference ofthe main valve member 32 is profiled to accept an upper diaphragmsupport washer 36 having a planar lower annular surface and a diaphragmretaining ring 38 having a planar upper annular surface. Sandwichedbetween the lower annular surface of upper diaphragm support washer 36and upper annular surface of diaphragm retaining ring 38 for movementwith the main valve member 32 is the central area of an annular flexiblediaphragm 17 which serves as a pressure member for the valve 10.

[0026] A bonnet plate 40 is secured to the top of the valve body 12 bysuitable fasteners 42. Disposed between the bonnet plate 40 and a raisedcircumferential ridge 44 on the top of the valve body 12 is the outercircumference of diaphragm 17 which is fixedly held on its top side bythe bonnet plate 40, and on its bottom side by the raisedcircumferential ridge 44 of the valve body 12 and a seal 46 inside andconcentric with the ridge 44. Seal 46 cushions the underside of thediaphragm 17 and prevents leakage of fluid at the interfaces between thebonnet plate 40, valve body 12, and diaphragm 17.

[0027] An annular retaining clip 48 captured in a groove circumscribingthe main valve member 32 urges the upper diaphragm support washer 36toward the central region of diaphragm 17 to secure diaphragm 17 againstdiaphragm retaining ring 38. The vanes 34 are notched to received anannular main valve seal 50 below retaining ring 38. Main valve seal 50is preferably fabricated from an elastomeric material.

[0028] The main valve unit 30 includes main valve member 32, upperdiaphragm support washer 36, diaphragm retaining ring 38, diaphragm 17,retaining clip 48, and main valve seal 50, all of which move toward andaway from the main valve seat 18 as a unit. During such movement, anintermediate annular portion 54 of diaphragm 17 is free to flex andstretch while the periphery of diaphragm 17 is held fixedly in place.Axial movement of the main valve unit 30 takes place with the vanes 34of main valve member 32 guided within a vertical cylindrical wall of theoutlet port 16 leading from the main valve seat 18.

[0029] Within the main valve member 32, running along its central axis,is a pilot passageway in the form of a circular bore 56 surrounded atits upper end by a pilot valve seat 58 and opening at its lower end intothe outlet port 16. The pilot passageway 56 is selectively opened andclosed by a pilot valve sealing member 68.

[0030] A main valve spring 60 is compressed between a shoulder 62 formedwith the bonnet plate 40 and the top surface of the upper diaphragmsupport washer 36 thereby urging the main valve unit 30 downwardly intoengagement with the main valve seat 18.

[0031] The fluid inlet port 14 is bounded by the underside of the mainvalve unit 30 (including diaphragm 17) and the exterior surface ofvertical section 28 of outlet port 16. A reservoir 64 occupies the openvolume above the main valve unit 30.

[0032] The diaphragm 17 is impermeable to the fluid to be controlled bythe proportional flow valve 10. A bleed passageway 66 in the bonnet 40and valve body 12 enables fluid communication between the reservoir 64and inlet port 14 so that fluid from the inlet port 14 can enter thereservoir 64 above the main valve unit 30. The bleed passageway 66 has asmaller cross section than the smallest cross section of pilotpassageway 56 so that fluid can flow through the pilot passageway 56faster than through the bleed passageway 66 when the pilot passageway 56is open.

[0033] When the pilot valve is closed, as shown in FIG. 1, i.e., whenpilot valve sealing member 68 engages pilot valve seat 58, and when themain valve is closed, i.e., when main valve seal 50 engages main valveseat 18, fluid cannot flow from the fluid inlet port 14 to the fluidoutlet port 16. When the pilot valve is open, i.e., when pilot valvesealing member 68 is not in engagement with pilot valve seat 58, and themain valve is closed, as shown in FIG. 2, a fluid can flow from thefluid inlet port 14 to the fluid outlet port 16 only through the bleedhole passageway 66 into the reservoir 64, and then from reservoir 64through pilot passageway 56. Such fluid flow is therefore limited to alow range of mass fluid flow rates, the actual rate of flow beingdependent on the relative time during which the pilot valve is openversus the time during which the pilot valve is closed.

[0034] When main valve seal 50 is out of engagement with main valve seat18, fluid flow can occur through the space between the vanes 34 of mainvalve member 32. The exposed area of the openings between the vanes 34increases as the main valve unit 30 rises thereby correspondinglyincreasing the rate of flow from the fluid inlet port 14 to the fluidoutlet port 16.

[0035] Initially, for example when the main valve member is removed fromthe main valve seat by a distance equal to or less than 25% of thediameter of the main valve opening, flow through the main valve openingis restricted and the rate of flow through the pilot opening constitutesmakes a significant contribution to the total rate of flow through thevalve, i.e., the sum of the mass flow rates through both the main valveopening and pilot valve opening. Under the above-described conditionwhere the main valve member is removed from the main valve seat by adistance equal to or less than 25% of the diameter of the main valveopening, mass flow through the valve can occur over an intermediaterange of rates, greater than the low range to which the valve isrestricted when flow is limited to the pilot opening.

[0036] Once the main valve member is removed from the main valve seat bya distance greater than 25% of the diameter of the main valve opening, ahigh range of mass flow rates is achievable. Flow at high rates occursprincipally through the main valve opening, and the amount of flowthrough the pilot opening becomes negligible.

[0037] In order to achieve low flow rates solely through the pilotopening of the valve, i.e., while the valve is in the state shown inFIG. 2, the pilot valve member is dithered onto and off of the pilotvalve seat by a current having a frequency and duty cycle which rapidlypermits and interrupts the flow of fluid through the pilot opening so asto maintain sufficient pressure in the reservoir 64 to prevent the inletpressure beneath the diaphragm from lifting the main valve member off ofthe main valve seat.

[0038] The rate of flow through the pilot opening need not be limited toa single magnitude. By varying the frequency and/or duty cycle of thepulse width modulated solenoid current, the relative time during whichthe pilot valve opening is exposed to fluid within the reservoir 64,versus the time the pilot opening is sealed by the pilot valve member,can be varied to continuously increase or decrease the rate of fluidflow through the pilot opening while preventing the pressure in thereservoir 64 from decreasing enough to permit the diaphragm be raisedfrom the main valve seat.

[0039] Depending on the frequency and pulse width of the solenoidcurrent, the valve will alternate between the off state shown in FIG. 1and the on state shown in FIG. 2 to permit low rates of fluid flowwithout opening the main valve, that is, without lifting the main valvemember from the main valve seat.

[0040] Surmounting the bonnet plate 40 is a solenoid actuator 70. Thesolenoid actuator 70 includes a coil 72 of electrically conductive wirewound around a spool 74 made of non-electrically and non-magneticallyconductive material. Suitable terminals are provided for connection to asource of electric current for energizing the solenoid coil 72. Ahousing 76 of magnetic material, surrounds the solenoid coil 72.

[0041] A stationary armature or plugnut 78 is located within the upperportion of the spool 74. A core tube 80 extends downwardly from theplugnut 78 and through the remainder of the spool 74. Surrounding thelower portion of the core tube 80 is a collar 82 which is, in turn,fastened to the upper portion of the bonnet plate 40. Fastening betweenthe core tube 80 and collar 82, and between the collar 82 and bonnetplate 40 can be by press fit, welding, crimping, threading or in anyother conventional manner of forming a sturdy and fluid tight connectionas will be known to those skilled in the art.

[0042] Slidably axially disposed within the core tube 80 is a movablearmature 84 of magnetic material. Mounted on the movable armature 84near its lower end is a circumferential flange 86. A pilot valve spring88 surrounding the movable armature 84 is compressed betweencircumferential flange 86 and the bottom surface of collar 82 and urgesthe movable armature 84 downwardly away from plugnut 78. The upper faceof the movable armature 84 and lower face of the plugnut 78 arecorrespondingly profiled so that the two faces mesh as the movablearmature 84 moves toward the plugnut 78. At its lower end, the movablearmature 84 carries the pilot valve sealing member 68 formed ofresilient material.

[0043] When solenoid coil 72 is deenergized (FIG. 1) and the fluid inletport 14 of proportional flow valve 10 is connected to a source ofpressurized fluid, e.g. a gasoline pump, the fluid is forced through thebleed channel 66 into the reservoir 64 above the main valve unit 30. Thearea of the top of the main valve unit 30 exposed to the fluid isgreater than the area of the bottom of the main valve unit 30 exposed tothe fluid. Hence, the force of the fluid on the top of main valve unit30, combined with the force of the spring 60, holds main valve seal 50against main valve seat 18 to close the proportional flow valve 10. Whensolenoid coil 72 is first energized by an electric current (FIG. 2),movable armature 84 is attracted to plugnut 78, and hence begins to moveupwardly against the force of spring 88. As movable armature 84 rises,it moves pilot valve sealing member 68 away from pilot valve seat 58,thereby permitting inlet fluid to flow through passageway 56 into outletport 16 which is at the lower outlet pressure. Because the effectiveflow rate through the pilot passageway 56 is greater than the effectiveflow rate through the bleed channel 66, the pressure above the mainvalve unit 30 and diaphragm 17 begins to decrease. Although the pilotopening in the illustrated preferred embodiment of the invention is oflarger diameter than the bleed opening, it is possible to have a greatereffective flow rate through the pilot opening than through the bleedopening even if the pilot opening has the smaller diameter when the flowchannels are such that turbulence retards the rate of flow through thebleed channel relative to the rate of flow through the pilot opening.

[0044] If the frequency and pulse width of the solenoid current aresufficient to raise the pilot valve sealing member 68 from the pilotvalve seat 58 for a large enough proportion of time, the upward force ofthe fluid inlet pressure on the main valve unit 30 begins to exceed thedownward force of the fluid pressure on the main valve unit 30, the mainvalve unit 30 begins to rise (FIG. 3), and main valve unit 30 moves awayfrom main valve seat 18. Main valve seal 50 disengages main valve seat18 and communication between fluid inlet port 14 and fluid outlet port16 through the spaces between vanes 34 of main valve member 32 isenabled, thereby initially permitting intermediate range fluid flow frominlet port 14 to outlet port 16.

[0045] The main valve unit 30 continues to rise until pilot valve seat58 engages pilot valve sealing member 68, i.e., the pilot valve isclosed. As a result, high pressure fluid cannot escape from thereservoir 64. As fluid entering the reservoir 64 builds up, the downwardforce on the main valve unit 30 increases until it, in combination withthe downward force of the spring 60, again exceeds the upward force ofthe inlet fluid against the bottom of main valve unit 30. The result isdownward movement of the main valve unit 30. However, as soon as themain valve unit 30 begins to move downwardly, pilot valve 68 opens, onceagain permitting high pressure fluid above the main valve unit 30 toescape through passageway 56 to the fluid outlet port 16. An equilibriumposition (FIG. 4) is quickly established in which main valve unit 30constantly oscillates a very short distance as pilot valve 68 isrepeatedly opened and closed.

[0046] The location of the main valve unit 30 as it oscillates isdetermined by the position of movable armature 84 and, hence, pilotvalve sealing member 68. This position also determines the spacingbetween main valve member 32 and main valve seat 18, and hencedetermines the rate of flow through the main valve opening.

[0047] Whether intermediate or high mass flow rates are obtained isdetermined by the extent to which the main valve member is raised fromthe main valve seat, which is in turn set according to the position ofmovable armature 84 is a function of the duty cycle and/or frequency ofthe pulse width modulated current applied to solenoid coil 72, thepreferred method of current control on solenoid activated proportionalflow control valves being by pulse width modulation (PWM).

[0048] With pulse width modulation, as employed in prior artproportional solenoid valves, a fixed frequency variable duty cyclesquare wave is applied to the coil of the solenoid in order to vary thecurrent in the coil in a linear fashion, thereby varying the forceexerted by the solenoid on the valve actuating mechanism, and thuschanging the flow through the valve. The use of a square wave signal hastwo distinct advantages over the use of a linear amplifier to control ofthe solenoid current. First, the switching type of controller has muchgreater efficiency than a linear amplifier. Second, the proper choice ofthe fixed switching frequency of the square wave can provide a smallvariation in solenoid current that translates into a mechanical ditherof the raised solenoid armature which, in turn, reduces the effects ofstatic friction and mechanical hysteresis in the valve. By carefullycontrolling the mechanical dither via pulse width modulation and/orfrequency modulation, selection of a desired rate of mass flow throughthe pilot opening is possible over a range of flow rates without openingthe main valve. This range is herein referred to as a low range of massflow rates.

[0049] Intermediate and high flow rates are achieved by increasing theduty cycle of the pulse width modulated solenoid current so that themagnitude of flow through the pilot opening is great enough to relievethe pressure in the reservoir above the main valve member therebypermitting the main valve member to rise off of the main valve seat.

[0050] If the pulse width modulation voltage has a 50% duty cycle, thecurrent flowing through the solenoid coil 72 will be 50% of maximum. Asa result, the movable armature 84 will rise though one half its maximumstroke between its position when the main valve is closed (FIG. 1) andits position when the valve is fully open (FIG. 4), i.e., when its upperface engages the lower face of the plugnut 78. Consequently, the mainvalve unit 30 will be permitted to rise through just 50% of its maximumrise, and hence main valve unit 30 will be spaced from main valve seat18 about ½ of the maximum spacing. Thus, approximately ½ of the rate ofmaximum flow through the valve will be permitted between fluid inletport 14 and fluid outlet port 16.

[0051] If the voltage is on 75% of the time and off 25%, i.e., there isa 75% duty cycle, movable armature 84 will rise through ¾ of its maximumstroke, and as a result approximately ¾ of the rate of maximum flowthrough the valve will be permitted between fluid inlet port 14 andfluid outlet port 16. It will be appreciated, therefore, that the rateof high volume flow through the main valve is proportional to the amountof current supplied to the solenoid coil 72.

[0052] Intermediate and high mass flow rates can be achieved dependingon the maximum stroke of the solenoid armature and the diameter of themain valve opening. For example if the pulse width modulation voltagehas a 25% duty cycle, the current flowing through the solenoid coil 72will be 25% of maximum. As a result, the movable armature 84 will risethough one quarter its maximum stroke. Consequently, the main valve unit30 will be permitted to rise through just 25% of its maximum rise andmain valve unit 30 will be spaced from main valve seat 18 about ¼ of themaximum spacing. If the diameter of main valve opening is greater than25% of the maximum stroke of the movable armature 84, flow will be inthe intermediate range.

[0053] When operated at high flow rates, i.e., whereat fluid flow isprimarily across the main valve seat, the valve of the instant inventionbehaves like the valve of U.S. Pat. No. 5,294,089. That valve is a fluidassisted design, which by the control of a small pilot orifice, allowsthe solenoid to effectively position the diaphragm which, in turncontrols the flow through a much larger orifice. This type of valvetypically has a turn down ratio of about 10 to 1 in flow over itscontrol range. As in the case of the aforementioned prior art valve,control of armature position is most precise when a pulsed DC source isapplied to the solenoid coil 72, as compared to simply varying theamplitude of a continuous DC current.

[0054] Prior art valves are operable only in the intermediate and highranges. Pulsing the current in such valves imparts a dither to themovable armature 84 with an amplitude that is very small in comparisonwith the displacement of the main valve member from the main valve seat.Hence the dithering has negligible effect on flow rate which isdetermined by the exposed area of the openings between the vanes 34, andwhich increases as the main valve unit 30 rises.

[0055] In the valve of the present invention, low rates of flow occursolely through the pilot opening. To achieve low flow rates over acontinuous range, the pulse width and frequency of the dithered pilotvalve sealing member are varied to determine the rate of fluid flowthrough the valve. It has been found that pulsing the pilot solenoidover a carefully controlled range of pulse durations will allow precisecontrol of flow through the pilot flow opening in the valve withoutcausing the diaphragm to open the main valve by raising the main valvemember from the main valve seat. By simultaneous variation of the pulsewidth and frequency of the wave form applied to the solenoid coil, aclose approximation of a linear correspondence between current and flowrate in the low flow range can be obtained, as it has heretofore beendone in the intermediate and high flow ranges. Moreover, the transitionfrom low flow range to the intermediate flow range can be madetransparent with no abrupt discontinuity in the current vs. flowcharacteristic, as can be done in the transition from the intermediateflow range to the high flow range.

[0056] For low flow rates, the on time of the pulse must be within arange that allows the solenoid to lift the pilot valve member from thepilot seat but does not allow the pilot valve member to expose the pilotopening sufficiently to cause the diaphragm to lift the main valvemember from the main valve seat. Also, the frequency of the currentapplied to the solenoid coil must be limited to a range over which thearmature of the pilot solenoid will continue to operate in a pulsingmode.

[0057] Balancing of three mechanical parameters enables achievement of acontinuous range of low flow rates, each of which can be selected bycontrolling the frequency and pulse wave duty cycle of the solenoid coilcurrent. These mechanical parameters are pilot orifice area, effectivebleed channel area and diaphragm hold down spring constant and springforce.

[0058] The area of the pilot orifice is a major controlling factor inachieving a wide range of low flow rates. As the cross sectional area ofthe pilot opening increases, so too does the range of available low flowrates or turn down ration of the low flow region of the current vs. flowrate characteristic.

[0059] The bleed channel of a proportional solenoid valve balances thepressures and forces above and below the diaphragm. The cross sectionalarea of the bleed channel is typically smaller than the cross sectionalarea of the pilot opening through the main valve member. Exposure of thepilot opening by lifting of the pilot valve member from the pilot valveseat causes a pressure imbalance across the diaphragm which urges thevalve main member away from the main valve seat. Conversely, sealing ofthe pilot opening balances the pressures on both sides of the diaphragmthereby allowing it to be closed in response to a mechanical force,e.g., from a spring. The size of the bleed channel is somewhat critical.If the bleed area is too small, pressure in the reservoir will decreaseso rapidly during the opening phase of the pulse cycle as to cause thediaphragm to lift the main valve member prematurely, thus limiting thehigh end of the low flow range. A bleed area which is too large, whilepotentially extending the flow range obtained by dithering the pilotvalve member onto and off of the pilot seat, would interfere with theneeded unbalancing of the pressures on either side of the diaphragm needfor displacing the main valve member from the main valve seat fortransition to the high flow range, i.e., across the main valve seat.

[0060] It has been found that by placing on top of the diaphragm, aspring having an appropriate spring constant and spring force, it ispossible to keep the main valve member in a closed position, i.e.,sealing the main valve opening, thereby allowing operation at higherduty cycles and frequencies, thus maximizing the low flow range.

[0061] By balancing solenoid duty cycle and frequency, pilot openingarea, bleed channel area, and diaphragm spring constant and springforce, high turn-down ratios, i.e., wide ranging flow rates, can beachieved by a single proportional solenoid valve.

EXAMPLE 1

[0062] In a proportional solenoid valve having a circular pilot opening0.078 inches in diameter, a bleed channel 0.073 inches in diameter, anda diaphragm hold-down spring with a spring force of 1.5 lbs. a low flowrange of 0.5-5.0 scfm was obtainable by varying the pulse width dutycycle and frequency of the solenoid coil current from 8% and 20 Hz to50% and 25 Hz, respectively. Depending on the size and design of thevalve, frequencies as high as 40 Hz or more, when combined withappropriate duty cycles, can be effective in obtaining low flow ratesover a substantial range.

[0063] Referring now to FIG. 5 of the drawings, a square-wave generator101 applies current in the form of pulsed DC signals to the coil 72 ofthe proportional valve solenoid 70. The duty cycle, i.e., the percentageof on-time vs. off-time for a single cycle of the square wave signal iscontrolled by a pulse width modulator 103 the construction of which willbe known to those skilled in the art. A frequency setting circuit 105 isalso provided for setting the number of cycles per second of the pulsedDC signal produced by the generator 101. The construction of thefrequency setting circuit will also be known to those skilled in theart.

[0064] A manual control device, e.g., the control lever on the handle ofa gasoline pump, can be mechanically linked to a transducer for sendingsignals to a digital microcontroller 107 which is connected to the pulsewidth modulator circuit 103 and frequency adjusting circuit 105 forsimultaneously adjusting the frequency and duty cycle of the DC pulsesapplied to the solenoid coil by the generator 101. The microcontroller107, pulse width modulator circuit 103, and frequency setting circuit105, may be designed and/or programmed so that narrow pulses areapplied, i.e., the pulsed waveform has a low duty cycle, for enablinglow flow rates at which time the solenoid armature is dithered forallowing flow only through the pilot opening of the proportional valvewhile preventing lift off of the main valve member from the main valveseat. Moreover, the duty cycle and frequency of the solenoid coilcurrent may be adjusted to increase the rate of flow through the pilotopening while still preventing main valve member lift-off. Flow rate isstill further increased by enlarging the duty cycle of the solenoid coilcurrent beyond a percentage whereat lift-off of the main valve memberfrom the main valve seat occurs.

[0065] It has been found that by employing an extended rangeproportional valve in accordance with the invention, a substantiallylinear relationship between flow rate and pump handle position may beachieved over a range from very low flow rates to very high flow rates,thereby enabling linear flow control over a turn-down ratio of as muchas 100 to 1 or more.

[0066] In designing an extended range proportional valve in accordancewith the invention, it is preferable to model the operation of the valveby examining the response of the valve to a PWM (pulse width modulated)control voltage that is applied to the coil of the solenoid operator.This voltage waveform causes a variation in the position of the armatureof the solenoid. The motion of the armature of the solenoid, in turn,causes a variation in rate of mass flow through the valve.

[0067] The motion of the armature can be described by a standard secondorder differential derived from a free body diagram of the armature andall relevant forces acting on it, including gravity, return springforce, and the magnetic force of attraction.

Md ² x/dt ² +Bdx/dt+Kx=F−F ₀

[0068] where

[0069] x=Displacement of the armature from its initial position inmeters

[0070] F=The magnetic attraction force on the armature in newtons

[0071] t=time in seconds

[0072] M=Mass of armature in kilograms

[0073] B=Friction force on the armature in newton/meter/sec

[0074] K=Spring constant of armature spring in newton/meter

[0075] F₀=The initial force on the armature that must be overcome tostart motion, in newtons

[0076] The dynamics of the electric circuit of the solenoid coil, whichis driven by the PWM excitation voltage, are described by the followingrelationships.

[0077] During the ‘ON’ period of the PWM signal

E=N dφ/dt+IR

[0078] During the ‘OFF’ period of the PWM signal

Ndφdt+IR=0

[0079] Where

[0080] Φ=Total flux in webers, which links the turns of the solenoidcoil

[0081] I=Coil current in solenoid

[0082] R=Resistance of solenoid coil

[0083] E=Voltage on solenoid coil when during on period of PWM signal

[0084] N=Number of turns in the solenoid coil

[0085] The coil current in the solenoid and the magnetic attractionforce on the armature in newtons are both functions of the total fluxwhich links the turns of the solenoid coil, and the displacement of thearmature from its initial position, i.e.,

I=f(Φ,x) and F=f(Φ,x)

[0086] Both of the above relationships are non-linear functions, thatare dependent upon the geometry of the solenoid operator and thematerials from which the valve components are constructed. Solutions tothe foregoing equations may be obtained by modelling the mechanical andelectrical elements of the valve on a digital computer by use of circuitsolver software, such as the commercially available SPICE program. Insuch a model, the electrical driver circuitry is directly modeled byelectrical elements, and the mechanical components are represented bycorresponding electrical analogs.

[0087] The magnetic coupling of back emf (Ndφ/dt), core position,current, and solenoid force can be modeled with the use of an elementthat accepts tabular data about the solenoid's parameters. This tabulardata can be extracted from a magnetic finite element analysis of thesolenoid over a range of operating conditions with solutions obtainedfor various values of core position and coil excitation. An example of acommercially available software solver capable of performing thisanalysis on a digital computer is EMSS by Ansoft of Pittsburgh Pa. Thissolver integrates magnetic finite element analysis programs with aversion of the SPICE program. By modeling this problem in such a solver,a solution in the form of a time variant waveform that represents thedisplacement x, i.e., the displacement of the armature from its initialposition, can be obtained.

[0088] In the range of low mass flow rates, the total mass flow throughthe valve is equal to pilot flow only. That is, the main valve memberremains seated on the main valve seat thereby preventing flow throughthe main valve opening. Using the displacement, x, as determined by thesolver, the mass flow of a gas or liquid through the pilot opening ofthe main valve member can be calculated from the followingrelationships.

[0089] Where the fluid passed through the valve is a gas:

M _(pilot(gas))=(K P ₁ C _(d) π x D ₁ N ₁₂)/(T ^(½)),

[0090] where

[0091] γ=gas constant

[0092] M=Mass flow per unit of time

[0093] Ro=degrees Rankine

[0094] x=Displacement of the armature from its initial position ininches

[0095] K=Constant (Ro^(½))/unittemp.=[(γ−1)/2γ/((P₁/P₂)^((γ−1)/γ)−1)]−(1γ)

[0096] P₁=Inlet pressure in psia

[0097] P₂=Pressure downstream of main valve seat

[0098] C_(d)=Discharge coefficient

[0099] D₁=Pilot sealing surface diameter

[0100] N₁₂=Ratio of actual flow to sonic flow per unit area at givenvalues of total temperature and pressure

[(P ₂ /P ₁)^(2/γ)−(P ₂ /P₁)^(((γ+1)/γ)/(γ−1)/2(2/γ+1))^((γ+1)/(γ−1)))]^(½)

[0101] T Inlet temperature in Ro

[0102] Where the fluid passed through the valve is a gas:

M_(pilot (liquid)) =C _(d) ×D ₁ (2g _(c) p (P ₁ −P ₂))^(½),

[0103] where

[0104] g_(c)=gravitational constant (386 in-lbm/lbf-sec²)

[0105] p=density (lbm/in³)

[0106] The total mass flow through the valve equals mass pilot flowuntil the displacement of the main valve member from the main valveseat, i.e., diaphragm stroke, X_(d)>0

[0107] In order to determine when the main valve member is lifted fromthe main valve seat, thereby unsealing the main valve opening forincreasing the mass flow rate through the valve, the relationshipbetween the changes in pressure, temperature and volume occurring withinthe valve can be considered as follows.

[0108] The Ideal Gas Equation is known to be

M=PV/RT

[0109] where

[0110] P=pressure in diaphragm chamber

[0111] V=volume in diaphragm chamber

[0112] R=perfect gas constant

[0113] M=mass of gas in diaphragm chamber

[0114] Taking the derivative of the Ideal Gas Equation:

m/M=p/P+v/V+t/T=0

[0115] Where

[0116] m=change in mass M

[0117] v=change in volume V

[0118] p=change in pressure P

[0119] t=change in temperature T

[0120] Assuming a polytropic process, the relationship of pressurechange to volume change is calculated from the following:

P=nPA _(d) X _(d) /V,

[0121] where

[0122] A_(d)=diaphragm area

[0123] X_(d)=diaphragm movement

[0124] n=number between 1 (for constant temperature) and γ (for constantentropy)

[0125] γ=ratio of specific heats

[0126] Solving for X_(d) gives the diaphragm displacement:

X _(d) =pV/nPA _(d)

[0127] By varying the duty cycle of the pulse width modulated current inthe solenoid coil, and/or the frequency of the current, to dither thepilot valve member onto and off of the pilot valve seat, mass flow ratescan be achieved over a continuous low range. When the rate of pilot massflow is increased to a magnitude whereat the differential pressureacross the main valve member causes it to be initially raised from themain valve seat, mass flow through the pilot opening in the main valvemember is supplemented by limited mass flow through the main valveopening which is partially blocked by the main valve member being inclose proximity to the main valve opening. While the main valve memberis displaced from the main valve seat a distance equal to or less than25% of the diameter of the main valve opening, mass flow rates over anintermediate range can be achieved. Once the main valve member is raisedfrom the main valve opening by a distance position greater than 25% ofthe diameter of the main valve opening, mass flow rates over a highrange can be achieved

[0128] Once the main valve opening is unsealed, the mass flow ratethroughout the intermediate range of flow rates can be calculated asfollows.

[0129] M_(total)=mass flow rate through the extended range proportionalvalve

M _(total@Xd>0.25 D2) =M _(diaphragm) +M _(pilot)

[0130] where

[0131] D₂=diameter of the main value opening

[0132] M_(diaphragm)=mass flow rate through the main valve opening

[0133] M_(pilot)=mass flow rate through the main valve opening

[0134] As main valve member displacement increases and the main valvemember is no longer in close proximity to the main valve opening, therate of mass flow through the pilot opening in the main valve memberbecomes insignificant relative to the rate of mass flow through the mainvalve opening and can be ignored. Hence, the mass flow rate throughoutthe high range of flow rates can be calculated as follows.

M _(total@Xd>0.25D2) =M _(diaphragm)

M _(diaphragm (gas))=(K P ₁ A ₁ N ₁₂)/(T ^(½))

M _(diaphragm (liquid)) =A ₁ (2g _(c) p (P ₁ −P ₂))^(½),

[0135] where

[0136] A₁=X_(d)C_(d)D₁π=effective area of main valve opening

[0137] The effective area of the main valve opening when the main valvemember is displaced from the main valve seat by less than 25% of thediameter of the main valve opening is equal to the area of the mainvalve opening across which an equal pressure drop occurs under similarconditions when the main valve member is sufficiently displaced from themain valve seat so as not to affect mass flow rate through the mainvalve opening.

EXAMPLE 2

[0138] In an extended range proportional valve that was constructed inaccordance with the preferred embodiment of the invention forcontrolling the flow of natural gas (methane gas constant used), thefollowing parameter values applied.

[0139] K=Gas constant (Ro^(½))/unit temp.=[((ratio of specific heats,γ−1)/2γ) ((P1/P2) (γ−1)/γ−1)]−(1/γ)=23.14

[0140] P₁=Inlet pressure in=79.7 psia

[0141] C_(d)=Discharge coefficient 0.35 (takes into account loss due toinlet restriction)

[0142] D₁=Pilot sealing surface diameter=0.056″

[0143] N₁₂=Ratio of actual flow to sonic flow per unit area at givenvalues of total temperature, and

[0144] pressure=P₂=0.95P₁=75.72 psia

[0145] Therefore

N ₁₂=0.4507 [(P ₂ /P ₁)^(2/y)−(P ₂ /P ₁)^((y+1)/y)/((y−1)/2(2/(y+1))^((y+1)/(y−1)))]^(½)

[0146] T=Inlet temperature in degrees Rankine (Ro)=527

[0147] C_(d)D₁=main orifice=0.328″−(0.1652 to 0.326)

[0148] M=Mass of armature in kilograms=0.0277

[0149] B=Friction force on the armature in newton/meter/second=9.0

[0150] K=Spring constant in newton/meter=2185

[0151] F_(o)=Initial force on the armature that must be overcome tostart motion, in newtons=1.338

[0152] R=Resistance of solenoid coil=6.5 ohms

[0153] N=Number of turns in the solenoid coil=850

[0154] It is to be appreciated that the foregoing is a description of apreferred embodiment of the invention to which variations andmodifications may be made without departing from the spirit and scope ofthe invention. For example, this invention could also be applied to apilot operated proportional solenoid valve design wherein pressure on arigid piston, instead of a flexible diaphragm, is used to lift the mainvalve member.

What is claimed is:
 1. A proportional flow valve for selectivelycontrolling the rate of flow of fluid over an intermediate range of massflow rates between a contiguous low range of mass flow rates and acontiguous high range of mass flow rates, comprising: a valve bodyincluding an inlet port, an outlet port, and a main valve seat mountedin said body and having an inlet side exposed to said inlet port and anoutlet side exposed to said outlet port, a main valve member movablymounted within said valve body into and out of engagement with the mainvalve seat to close and open the valve, said main valve unit having apilot opening extending therethrough and a pilot seat surrounding saidpilot opening, a pilot valve member movably mounted within said valvebody into engagement with the pilot seat for sealing the pilot openingthereby preventing fluid flow from said inlet port to said outlet portthrough said pilot opening and out of engagement with the pilot seat forexposing the pilot opening thereby permitting fluid flow from said inletport to said outlet port through said pilot opening, a solenoid actuatorhaving an armature on which said pilot valve member is mounted formovement therewith, and a coil for producing a flux as a function of anelectrical current flowing therein, said armature being movable inresponse to said flux, and alternating current electrical energizermeans operatively connected to said coil for selectively inducingtherein an alternating current having a characteristic with a magnitudeselectable from a range of magnitudes for disengaging said pilot valvemember from said pilot valve seat for a time long enough to causesufficient flow of said fluid through said pilot opening for creating adifferential pressure across said main valve member sufficient todisengage said main valve member from said main valve seat by a distanceequal to a fraction of a diameter of said main valve opening for causingflow of said fluid through said pilot opening at a mass flow rate insaid intermediate range of flow rates.